This invention pertains to protractors. It pertains particularly to scribing protractors of the class used for determining the angle with reference to the vertical of a surface to be measured, and for marking the location of the angle on the surface.
In the welding, carpentry and metal working trades there are many situations in which it is necessary to secure an accurate angular measurement of difficult surfaces.
Thus in the welding trade it frequently is necessary to measure angles on the exterior surface of a pipe in order to join the ends of two pipes together, or to splice the end of a second pipe in a selected position on the surface of a first pipe.
In the metal working trades it is frequently necessary to lay out an angle on the surface of angle iron, bar stock or plate.
In the carpenter's trade it frequently is required to determine the angle of horizontal, vertical and angular surfaces.
Prior art patents addressed to the problem of providing a protractor suitable for use in such situations include the following:
______________________________________ U.S. Pat. No. Inventor Title ______________________________________ 279,336 Clark, W. H. Apparatus for Marking Angular Cuts in Sheet Metal Pipes 1,318,607 Schreiber, C. Protractor 2,729,891 Winter, C. C. Compass Instrument for Measuring and Marking Uneven Surfaces ______________________________________
None of the above patents, nor any patent, publication or prior art device known to me, provides a protractor of simple and durable construction, which is useful in a wide variety of angle-measuring situations, which is easily used with a minimum of training and experience, which may be used to determine angles quickly and with a high degree of accuracy, and which is provided with integral means for marking the angle so determined.
It is the general purpose of the present invention to provide such a protractor.
This purpose is accomplished by the provision of a protractor which, broadly considered, comprises a case having a base adapted to be placed in contact with a surface to be measured, a dial calibrated in selected units of angular measurement mounted in the case, and plumb or counterweighted needle means pivotally mounted in the case overlying the dial for determining the angle of the surface to be measured with reference to the vertical. Scribing means are mounted on the case for marking the position of case contact with the surface to be measured after the case has been adjusted to give the desired reading of angular measurement on the dial.